1. Field of the Invention
This invention relates to aqueous dye baths containing mixtures of compatible acid dyes, some of which are novel, which are useful for dyeing deep-dyeing nylon fibers.
2. Description of the Prior Art
Nylon styling yarns have increased in commercial importance in recent years because of their physical and chemical durability and their multicolor dyeability. Such properties are especially desirable in carpet fibers. Nylon styling yarns generally consist of fibers of an acid-modified (anionic) nylon containing sulfonic acid groups which make the fibers receptive to basic dyes and two or more unmodified nylons which differ in their amine end group content and hence their receptivity to acid dyes. Such yarns are known to be dyeable both by exhaust and continuous methods. In the carpet industry such yarns in the form of bulked continuous filament (BCF) yarns may be dyed with combinations of basic, acid and disperse dyes. Basic (cationic) dyes which have good application and fastness properties on acid-modified nylon and which reserve, that is, produce little or no stain on, unmodified nylons under the neutral to weakly acidic conditions used to dye nylon styling yarns are readily available commercially. Also readily available are monosulfonated acid dyes which reserve acid-modified nylon while producing light to heavy shades of good fastness properties on unmodified nylons, the shade depending on the amine end group content of the unmodified nylon. Light-dyeing nylons are generally recognized in the art as having an amine end group content of 25 gram equivalents or less per million grams of the polymer; deep-dyeing nylons generally contain 70 or more gram equivalents of free amine end groups per million grams of the polymer; and medium-dyeing nylons contain an intermediate number of amine end groups, generally about 40-50 gram equivalents per million grams of the polymer. Disperse dyes can be used to dye acid-modified and all types of unmodified nylon fibers to the same degree. It can be seen, therefore, that a combination of basic, acid and disperse dyes can be employed to achieve a broad range of color effects on nylon styling yarns. This range can be broadened by using disulfonated or monosulfonated/monocarboxylated dyes instead of the aforesaid monosulfonated dyes. Such dyes have considerably more affinity for deep-dyeing nylons and produce a much greater shade contrast between these fibers and light-and medium-dyeing nylons than is possible with monosulfonated dyes. In practice, the selection of dyes containing two functional acidic groups for use on nylon styling yarns is extremely difficult. Although such dyes may have adequate buildup and lightfastness on deep-dyeing nylon in self-shades and show good reserve of light-dyeing and acid-modified nylons, they may exhibit a blocking action on each other when applied from the same dye bath. In other words, one diacidic dye may preferentially dye deep-dyeing nylon and prevent another such dye from exhausting completely onto the substrate, in which case unlevel dyeings may be produced and the anticipated mixed shade may not be obtained. In the continuous dyeing of tufted nylon styling yarn carpeting, the use of diacidic dyes which exhibit the incompatibility described above may result in tippy dyeings (tippiness) wherein the top of the tuft is different in shade from the bottom.